1. Field of the Invention
The present invention relates to an electronic copying machine equipped with a cleaner of the blade type.
2. Description of the Prior Art
As shown in FIG. 1a, conventional blade-type cleaners for electronic copying machines comprise a blade member 2 of polyurethane rubber or like elastic material which is held pressed in contact with the surface of the photoconductive drum 1 to scrape residual toner off the surface of the drum 1 during the rotation of the drum 1.
In such blade type cleaners, the blade member is adapted to be pressed against the surface of the photoconductive drum by a constant force to clean the drum surface effectively. During cleaning, the blade member must be held in suitable sliding contact with the drum surface to avoid damage to the drum surface or to the blade member. This is assured by suitably determining the force to achieve the desired pressing contact of the blade member, hardness of the rubber, the angle of contact of the member, etc. However, such conditions are usually determined according to the frictional force to be obtained by the contact between the drum and the blade member during use, so that, for example, when the drum or the blade member is replaced by a new one or when the machine is started into operation for the first time (this state will hereinafter be referred to as the "initial state"), an abnormally great friction function is likely to act between the drum surface and the blade member without permitting the desired sliding contact. Especially when a selenium-type photoconductive drum is placed into use for the first time, the drum surface, which is nearly specular, produces a great frictional force. In such an initial state, the drum or blade member is liable to be damaged, to produce abnormal noises or to develop other troubles. Thus the initial operation involves a serious problem.
With respect to damage to the blade edge, when a blade is pressed against a photoconductive drum, there is ideally line contact therebetween, but because the material of the blade is somewhat compressed, there is actually surface-to-surface contact of the blade with the drum (see FIG. 1b), whereupon surface attraction between the two members causes them to tend to adhere to each other. When the drum is rotated in this state, a maximum force of static friction is produced due to the friction between the two members, causing the blade edge portion to undergo plastic deformation exceeding the elastic limit of polyurethane rubber and thus rupture (FIG. 1c). The heat of evolved at this time due to the friction further deforms the blade. These phenomena cause damage to the blade edge. Surface contact is more likely to occur when the drum has a specular surface and also when the blade edge has a lower hardness.
The edge portion of such a blade has been examined microscopically, and it has been found that the edge had developed a roughness of about 20 to about 30.mu. over the entire length thereof.
With respect to abnormal noise, when undergoing plastic deformation as described above (FIG. 1c), there is an abnormally increased force of friction produced, acting to brake the drum against rotation and creating an abnormal noise. Accordingly the damage to the blade and the abnormal noise are concurrent.
The damage to the blade further tends to mar and damage the surface of the drum.